1. Field of the Invention
The present invention relates to a pneumatic tire having a sipe cut into a land portion formed in its tread surface, and more particularly to a pneumatic tire useful as a studless tire.
2. Description of the Related Art
Generally, a studless tire has a sipe cut into in a rib or a block as a land portion formed in a tread surface, and thus increases a water removing effect of the sipe and an edge effect of a sipe edge to increase braking performance on an icy road (ice braking performance).
However, in the pneumatic tire, the increasing of the number of sipes formed in the land portion causes a land piece surrounded by the sipes to be easily deformed by a load applied to the tire. Thus, adjacent land pieces are brought into tight contact with each other to close the sipe and reduce the edge effect and the water removing effect of the sipe, thereby preventing sufficient ice braking performance from being provided.
To solve the above-described problem, for example, in Japanese Patent Laid-Open No. 9-272312, a wide section is formed that is a part of a sipe extended from a tread surface to a sipe groove bottom with a fixed width, and thus the wide section is always opened even when the sipe is closed, thereby ensuring a water removing effect and an edge effect for the purpose of the increasing of ice braking performance.
However, in Japanese Patent Laid-Open No. 9-272312, the wide section is formed from the tread surface to the sipe groove bottom with the fixed width, which may easily reduce the rigidity of its land portion (rib or block). Particularly, when a plurality of wide sections are formed in one sipe to sufficiently ensure a water removing effect and an edge effect of the sipe, the rigidity of the entire land portion is significantly reduced. Thus, in Japanese Patent Laid-Open No. 9-272312, when a large load is applied to a tire, the land section is excessively deformed to reduce the edge effect and the water removing effect to the contrary. Also, when the wide section is formed in a land piece between sipes, there is a large difference between a low rigidity portion and a high rigidity portion in the land piece, which may easily cause uneven wear on a land piece between the sipes and reduce anti-wear performance.
Thus, in view of the above-described problems, the present invention has an object to provide a pneumatic tire having a sipe, which can increase ice braking performance without reducing anti-wear performance.